#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<string.h>
#define MAX 1000 
int main()
{
    int m = 0, n;
    char num1[MAX], num2[MAX], sum[MAX];
    scanf("%s", num1);
    scanf("%s", num2);
    n = strlen(num1);
    for (int i = 0; i < n; i++)
    {
        if (num1[i] != num2[i])
        {
            sum[m++] = i;
        }
    }
    int flag = 0;
    for (int i = 0; i <= m; i += 2)
    {
        flag += sum[i + 1] - sum[i];
        if (sum[i + 1] = NULL)
        {
            flag += 1;
        }
    }
    printf("%d", flag);
    return 0;
}